Check wiring harness around and including plug to the coil pack. Also check fuel pressure with vehicle running. I'm not sure of the specs but, Iit should be around 35 to 40 psi. at idle, and 50 to 75 at higher RPM's. I've seen Fords run with a bad fuel pump and demonstrate these exact symptoms
Testimonial: "I'll give that a try. It does seem to run better when the fuel level is low!? This vehicle does have 190,000 k on it which is why I was thinking the cats could be clogged too. Thanks again!"
SOURCE: vehicle came in for check
A misfire at idle that smooths out at cruise is ALMOST ALWAYS caused by a vacuum leak. Take a hard look at your fuel trims at idle. If the Bank 2 Long Term Fuel Trim is more than + a couple points higher than the Bank 1 trim, your problem is most likely a vacuum leak. If the Fuel Trims even-out while holding the engine at 2000 RPM for about 20 seconds, then a vacuum leak is DEFINITELY your problem. I would suspect a leaking lower intake gasket leak because an upper plenum leak will normally affect all cylinders.
SOURCE: heavy idle, random misfire code 04 trailblazer
I would start with the inlet manifold gasket, these are know to break down causing vacuum leaks which can cause this issue, also check around engine for other vacuum leaks
SOURCE: code p0303
SWAP COIL PACKS to another Cylinder... See if it Follows the Coil Pack
2nd, Swap the INJECTOR to another Cylinder.. See if it follows the Injector.
You will get your Answer
There are few possibilities that can cause engine misfire
issues. It can be issue with spark plugs or faulty spark plugs. Also get the
compression test done for cylinders. If any of cylinder shows low compression
then required, then that particular cylinder will cause misfire.
Also get obd codes scanned, the error code will let you know
which cylinder is misfiring or all cylinders are misfiring.
-----------
For your trouble shooting I suggest you to refer the help
oinks below. It has step by step details for many engine misfire issues.
----------
Click the link below:-----
Ford Explorer Cylinder Misfire?
http://whoisbyme.blogspot.in/2012/06/ford-explorer-cylinder-misfire.html
---------
Engine Misfire codes on Chevrolet Malibu?
http://schematicsdiagram.blogspot.com/2011/12/engine-misfire-codes-on-chevrolet.html
---------
Cylinder 6 Misfire?
http://howtobyme.blogspot.com/2011/12/cylinder-6-misfire.html
------------
Misfire on cylinder 4?
http://schematicsdiagram.blogspot.com/2011/12/misfire-on-cylinder-4.html
-----
While stop engine idles like cylinder missing?
http://schematicsdiagram.blogspot.com/2012/01/while-stop-engine-idles-like-cylinder.html
----------
Ford Explorer 5.0L: Engine Miss?
http://whoisbyme.blogspot.in/2012/06/ford-explorer-50l-engine-miss.html
-----------
Oil on spark plugs and car misfires?
http://technoanswers.blogspot.in/2012/02/oil-on-spark-plugs-and-car-misfires.html
------------
Can cylinder misfire Damage the Catalytic converter?
http://schematicsdiagram.blogspot.in/2012/02/can-cylinder-misfire-damage-catalytic.html
------------
Car misfires and error code P0306 and P0303 is shown?
http://technoanswers.blogspot.com/2012/01/car-misfires-and-error-code-p0306-and.html
-----------
Chevrolet K1500 No spark, random misfire
http://repairhelpcenter.blogspot.com/2012/11/chevrolet-k1500-no-sparkrandom-misfire.html
-------------
2004 Ford F150: Engine Misfire and Lean Code?
http://whatisbyme.blogspot.in/2012/05/2004-ford-f150-engine-misfire-and-lean.html
-----------
1995 Toyota LS: Misfire at idle or low RPM
http://whatisbyme.blogspot.in/2012/04/1995-toyota-ls-misfire-at-idle-or-low.html
--------------
Toyota Corolla:
Random Misfire?
http://technoanswers.blogspot.in/2012/04/toyota-corolla-random-misfire.html
----------
2006 Ford Freestar: Misfire on Cylinder Number 2?
http://whatisbyme.blogspot.in/2012/06/2006-ford-freestar-misfire-on-cylinder.html
-----------------------------
This will help.
Thanks.
It can be issue with spark plugs or faulty spark plugs. Also
get the compression test done for cylinders. If any of cylinder shows low
compression then required, then that particular cylinder will cause misfire.
Also get obd codes scanned, the error code will let you know
which cylinder is misfiring or all cylinders are misfiring.
-----------
For your trouble shooting I suggest you to refer the help
oinks below. It has step by step details for many engine misfire issues.
----------
Click the link below:-----
Ford Explorer Cylinder Misfire?
http://whoisbyme.blogspot.in/2012/06/ford-explorer-cylinder-misfire.html
---------
Engine Misfire codes on Chevrolet Malibu?
http://schematicsdiagram.blogspot.com/2011/12/engine-misfire-codes-on-chevrolet.html
---------
Cylinder 6 Misfire?
http://howtobyme.blogspot.com/2011/12/cylinder-6-misfire.html
------------
Misfire on cylinder 4?
http://schematicsdiagram.blogspot.com/2011/12/misfire-on-cylinder-4.html
-----
While stop engine idles like cylinder missing?
http://schematicsdiagram.blogspot.com/2012/01/while-stop-engine-idles-like-cylinder.html
----------
Ford Explorer 5.0L: Engine Miss?
http://whoisbyme.blogspot.in/2012/06/ford-explorer-50l-engine-miss.html
-----------
Oil on spark plugs and car misfires?
http://technoanswers.blogspot.in/2012/02/oil-on-spark-plugs-and-car-misfires.html
------------
Can cylinder misfire Damage the Catalytic converter?
http://schematicsdiagram.blogspot.in/2012/02/can-cylinder-misfire-damage-catalytic.html
------------
Car misfires and error code P0306 and P0303 is shown?
http://technoanswers.blogspot.com/2012/01/car-misfires-and-error-code-p0306-and.html
-----------
Chevrolet K1500 No spark, random misfire
http://repairhelpcenter.blogspot.com/2012/11/chevrolet-k1500-no-sparkrandom-misfire.html
-------------
2004 Ford F150: Engine Misfire and Lean Code?
http://whatisbyme.blogspot.in/2012/05/2004-ford-f150-engine-misfire-and-lean.html
-----------
1995 Toyota LS: Misfire at idle or low RPM
http://whatisbyme.blogspot.in/2012/04/1995-toyota-ls-misfire-at-idle-or-low.html
--------------
Toyota Corolla:
Random Misfire?
http://technoanswers.blogspot.in/2012/04/toyota-corolla-random-misfire.html
----------
2006 Ford Freestar: Misfire on Cylinder Number 2?
http://whatisbyme.blogspot.in/2012/06/2006-ford-freestar-misfire-on-cylinder.html
-----------------------------
This will help.
Thanks.
A code P0303 may mean that one or more of the following has happened:
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